1 2 KANSAS UNIVERSITY QUARTERLY. 



McClung,^'^ in a later paper, describes the accessory chromosome as 

 occurring in Hippiscus. In the spireme stage it is to be seen as a 

 large, densely staining homogeneous body, in close contact with the 

 nuclear membrane. In a later stage it leaves its peripheral position 

 and takes on the appearance of a longitudinally split rod. It is di- 

 vided by the first maturation mitosis, but in the second passes over 

 bodily into one of the daughter cells. In Scolopendra, as far as I 

 have observed, the accessory chromosome shows no sign of division in 

 the prophase and goes to the equatorial plate as a spherical body. 



Sutton,^*' in his article on "The Spermatogonial Divisions in 

 Brachystola magna" describes the behavior of this element in the 

 spermatogonia. He throws much stress on the individuality of this 

 element, for, as he conclusively shows, "It maintains throughout the 

 spermatogonial divisions, as well as those which follow, an indubitable 

 independence, being enclosed at all stages, except those of actual di- 

 vision, in its own individual membrane.*' As I have shown, quite a 

 different condition exists in the pseudo-germinal-vesicle stage of 

 Scolopendra, for at this stage all the chromatin of the cell is con- 

 densed into one deeply staining, homogeneous mass. 



Montgomery,^' in his article on Peripatus, fails to find an accessory 

 chromosome, but describes a body which behaves very much like this 

 element. He gives at length his reasons for not considering it the 

 "chromatin nucleus." However, I believe he is mistaken, and that 

 the element described is, in truth, the accessory chromosome. 



In comparing the accessory chromosome found in Scolopendra 

 with that described by these investigators, several points of difference 

 are observed as well as many points of similarity. Its origin, staining 

 reaction and its behavior in the early spermatocytes are very similar 

 to that in insects, but in its behavior in the pseudo-germinal-vesicle 

 stage, and in the succeeding stages, it is quite different. As I have 

 shown, it seems to act as a reservoir in which is deposited practically 

 all of the chromatin of the nucleus. At this stage it is enormous as 

 compared with its former size. In the later prophase, part of the chro- 

 matin forming this mass leaves the accessory chromosome and col- 

 lects in diffuse granular masses, which eventually form the tetrads as 

 described. At this time the accessory chromosome loses its regu- 

 lar outline and becomes granular toward the outside. When the 

 tetrads are formed, however, it again assumes its homogeneous char- 

 acter and regular outline, but has decreased in size until it is no larger 

 than the ordinary chromosome in the metaphase. It can be readily 

 distinguished from the other chromosomes up to the time of the dis- 



15. McClung, C. E., 1900, loc. cit. 



16. Sutton, W. S., 1900, loc. cit. 



17. Montgomery, T. H., jr., 1901 : "The Spermatogenesis of Peripatus up to the Formation 

 of the Spermatid." Anat. An. Bd. XVI. 



